Prosecutors charged with investigating hundreds of cases of disappearances and mass killings of civilians in this Andean department say they do not have the power to force the military and police to respect legal processes, including provision of information on prisoners.

Since 1983, the Ayacucho prosecutor's office has received more than 1,000 reports of disappearances or irregular detentions attributed to government forces fighting the Shining Path leftist guerrillas.

Appointed by an independent attorney general under the democratic government of President Fernando Belaunde Terry, the prosecutors are charged with investigating the cases as well as hundreds of deaths of civilians.

The prosecutors say their work has been obstructed by the military, making it impossible to determine the fate of most disappeared persons or place responsibility for the mass graves discovered in the area.

"We would have to have cannons, missiles or sorcerers to work miracles to know where the disappeared are," said Juan M. Cravero Tirado, Ayacucho's chief prosecutor. "The military has no interest in collaborating with us, and we have no way of forcing them."

"People keep arriving here to see if we know something about disappeared persons," Cravero said. "We don't know anything, and that's all there is to it."

The apparent powerlessness of civilian legal authorities in Ayacucho is an indication of how the government of Belaunde, long considered one of Latin America's premier democratic politicians, has come to be charged with some of the area's most serious current rights violations.

Belaunde has struggled since his election in 1980 to rebuild democracy in Peru after 12 years of military rule. In July, he expects to become the first elected president to yield power to an elected successor in more than 60 years.

However, the president's record has been tarnished by mounting evidence that the military forces he placed in charge of nine provinces of Ayacucho and two neighboring departments almost 27 months ago have replaced the normal guarantees of democratic institutions with brutal tactics of repression.

"The killings, disappearances, and torture make it clear that the government of Peru is fighting terror with terror," said a recent report by Americas Watch, the New York-based human rights group. "Unfortunately, . . . the government of Belaunde has not provided leadership. Indeed, it has abdicated authority."

While local and international human rights groups have complained of abuses by the Ayacucho-based security forces for several years, the evidence of the reported violations has grown dramatically during the past six months.

Since August, a number of unmarked mass graves have been discovered around Ayacucho, containing up to four dozen bodies marked with evidence of torture and summary execution. In October, prosecutors publicly reported evidence that a group of police massacred 34 civilians in November 1983 in the village of Soccos.

London-based Amnesty International issued a report in January summarizing 1,005 cases of disappearances in the Andean provinces, as well as 420 cases of persons found dead after they were detained by police and soldiers.

Belaunde angrily has rejected reports of abuses and accused their authors of forming part of an international Marxist campaign to destabilize Peruvian democracy.

Prime Minister Luis Percovich has sought to discredit the Amnesty report, saying 54 of the alleged disappeared recently registered to vote in April's general elections. Nevertheless, the government's human rights record in Ayacucho has become a major political issue.

The reports of abuses also have become a source of concern for the Reagan administration, which has proposed increasing military aid to Peru from $8 million this fiscal year to $28 million in the next. Some diplomats and sympathetic politicians here say Belaunde is concerned about the reports of abuses but is unable to check the military forces he appointed to control the Andean provinces in December 1982 under a state of emergency.

There is a dramatic contrast between the emergency zones in the Andes and in the eastern jungle area of Tingo Maria and the bulk of Peru that is ruled by the civilian ministers of Belaunde. Throughout the country, political parties ranging from the right to the Marxist left are openly campaigning for elections in April. The government's tolerance for free speech and press freedom rivals that of the United States and other western countries.

This flourishing democratic climate is strangely inverted, however, in this isolated Andean region, where human rights activists have been arrested, leftist organizers have disappeared and civilian authorities cite threats both from the guerrillas and military forces.

A burgeoning movement of relatives of disappeared persons is based in Ayacucho, and outsiders visiting government offices frequently are besieged by poor Indian peasants from the countryside who desperately circulate through the town with crumpled photos and legal papers documenting the disappearance of a relative.

Even as the government in Lima heatedly disputes the legitimacy of human rights charges, prosecutors and other authorities here readily agree that elements of the police and military are responsible for the majority of disappearances and executions of civilians.

The problem, prosecutors say, is that they have been unable to pursue investigations of such cases. "When we have a report of a disappearance, we ask the military command for information," said Cravero. "If they say they are not holding the person, there's nothing more we can do."

In investigating reports of killings of civilians or mass graves, prosecutors are dependent on the local military command for transportation to the sites and protection in the countryside. But officials said the military has refused to provide such support in some cases and also has denied access to military bases where prisoners are held.

Many of the prosecutors themselves seemed to have despaired at their predicament. Four chief prosecutors have resigned in Ayacucho since 1983, complaining of their lack of authority. Those who remain seem to believe that even as representatives of a democratic government, they can do little to check the abuses.

"We can't even give the military suggestions," said an official in the provincial capital of Huanta, north of Ayacucho. "And if we push too hard, someone will come and get us in the night, and our bodies will just turn up with the others on the road the next morning."